1. Field of the Invention
This invention relates to a spigot and socket connection and in particular to a fitting for a spigot and socket connection such as a pipe joint in which engagement of the spigot within the socket is achieved by the application of a deforming or crimping force to a deformable region of the socket so that it engages the spigot received within it without either the application of heat or the continuing presence of any permanent independent retention means, for example, a screw fastener. The invention also relates to a method of forming such a spigot and socket connection and a tool for applying the deforming or crimping force to the deformable region of the socket.
2. Description of the Prior Art
British Patent Specification No. 856,610 discloses a tube coupling in which a joint is formed by radial compression of a sleeve onto a tube end, by for example a cable joining tool, and local sharp-pointed engaging elements in the initial annular clearance space between the sleeve and the tube end positively interengage in the deformations produced by the radial compression to form rigid unit resistant to compression of the joint.
In British Patent Specification No. 1,267,037, a method of forming a crimped tube joint is described in which a plain cylindrical sleeve is deformed by crimping it between two semi-cylindrical crimping surfaces which when brought together define a cylindrical crimping surface having a diameter less than the initial external diameter of the sleeve. The difficulty of radially compressing such a sleeve to cause uniform sleeve contraction is acknowledged and discussed and in cases where a large amount of compression is required, the method disclosed necessitates progressive compression of the sleeve in a plurality of successive steps employing a series of sets of compressing jaws of progressively smaller diameters of crimping surface in their closed condition.
In the pipe coupling of British Patent Specification No. 1,542,847, a weakened section of a screwed sleeve is deformed after assembly of the joint by a tool having rotary working elements to provide a positive grip between the sleeve and the pipe received in it. The connection between fluids conduits described in British Patent Specification No. 1,053,629 employs a plastics sleeve which is retained on a pipe received within it by the application of crimping pressure to a ductile metal sleeve surrounding the plastics sleeve in its pipe-receiving region. British Patent Specification No. 1,095,683 discloses a tool of relatively complex construction for forming such a connection.
The cylindrical sleeve connector of British Patent Specification No. 1,436,723 has one or more external annular grooves of a width specified in relation to the buckling profile of the wall in the region of the groove(s), so that they will deform radially inwardly in a predetermined manner to engage a pipe received within the sleeve by the application of an axial compressive force to the sleeve. The sleeve disclosed in British published Patent Application No. 2,032,558 A employs internal gripping ridges to ensure retention of a tube being gripped within the sleeve, while in the connection described in British published Patent Application No. 2,090,930 A, the plain cylindrical sleeve may be crimped at a number of points along its axial length and a polymer film interposed between sleeve and tube to ensure a seal.
In these connections of the prior art, the measures adapted to ensure integrity of the joint include the provision of internal engaging elements and the application of high crimping forces using special tools of complicated construction and large dimensions. The use of plain cylindrical fitting allows the location of crimping along the axial length of the fitting to be varied so that consistent and uniformly repeatable joints may not readily be achieved.